Spatial Variation of Bacterial Communities on the Leaves of a Southern Magnolia Tree

Nguyen, Emily Q.
(2017)
Spatial Variation of Bacterial Communities on the Leaves of a Southern Magnolia Tree.
Undergraduate thesis,
under the direction of Colin Jackson from
Biology,
The University of Mississippi.

Abstract

The leaf surface, or phylloplane, is a dynamic environment for its microbial inhabitants, which can be subjected to many environmental factors. Existing phylloplane studies have focused on differences in bacterial community structure between trees of the same species, in different geographical locations, or between trees of different species. Few studies have examined the spatial distribution of bacterial communities on the leaves of a single tree. In this study, leaf samples from different areas of the canopy were obtained from a single Magnolia grandiflora tree. Samples were taken from the high (3.5-4.0 m above the ground), middle (1.5 m), inner middle (1.5 m but close to the trunk), and low (0.5 m) portions of the tree canopy, following cardinal directions (north, south, east, west). Following DNA extraction procedures, dual index barcoding was used to sequence the V4 region of the 16S ribosomal RNA gene. Phylloplane communities were dominated by Alphaproteobacteria, Actinobacteria, and Bacteroidetes, which are common inhabitants of plants. Patterns in alpha and beta diversity suggested that the height from which the sample was taken had a strong influence on the shaping of communities, while cardinal direction was not a significant predictor of diversity. Interestingly, the inner leaves of the canopy had higher species abundance than the leaves on the outside of the canopy, which could suggest that the surrounding canopy protects the inner leaves from ultraviolent light, desiccation, or other factors that may limit bacterial growth.